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Remove email alias and assign to other shared mailbox

Medium Priority
Last Modified: 2019-08-14
Hi Experts,

In my Office365 tenant I have two domains registered. For the accounting department I want to have two separate shared mailboxes: accounting@domain1.com and accounting@domain2.com.

I have created the mailboxes accounting.domain1@domain1.com and accounting.domain2@domain1.com. Now I want to add the mail aliases (should be the reply addresses) accounting@domain1.com and accounting@domain2.com.

The problem is that after I have created accounting@domain1.com it already includes the smtp address accounting@domain2.com. I then obviously get an error when I want to assign accounting@domain2.com to the mailbox accounting.domain2@domain1.com.

How can I remove the alias accounting@domain2.com from accounting.domain1@domain1.com and assign it to accounting.domain2@domain1.com?

I tried Powershell Set-Mailbox -Identity "accounting domain1" -EmailAddresses @{remove="accounting@domain2.com"} but it does not do anything.

Thanks for the help in advance,

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MichelangeloSystem Administrator / Postmaster

Can you explain why is the proxyaddress  accounting@domain2.com 'already included'  to the first shared mailbox? Is it an hybrid environment? Domain1 and domain2 are your own domains or onmicrosoft domains?


Hi Michelangelo,

We previously wanted to have both mail addresses in one mailbox. Afterwards the decision was made to split into 2 separate mailboxes. This is when the problem occurred.

But I have found the solution to my problem described here https://office365.uservoice.com/forums/264636-general/suggestions/13290942-unable-to-remove-default-domain-email-address-adde

These Exchange online powershell commands that were needed
Set-Mailbox accounting.domain1@domain1.com -MicrosoftOnlineServicesID accounting.domain1@domain1.com
Set-Mailbox accounting.domain1@domain1.com -EmailAddresses @{remove="accounting@domain2.com"}

Then accounting@domain2.com is free to be used for the other mailbox.

Thanks for the help.
MichelangeloSystem Administrator / Postmaster

Well that's good! Just assign the solution to yourself then, this thread is good as reference for people with the same issue.
The solution is described in the tread.